The present invention relates generally to projection systems that use pixels and, more particularly, to the use of combined opto-mechanical and computer systems for improving the apparent number of pixels of projected images.
Liquid Crystal Display (LCD) projectors are a common form of projection system which use pixels to project an image. LCD projectors typically consist of a source of light and three LCD panels which are optically coupled to produce a color image. Each LCD panel projects one of the primary colorsxe2x80x94red, green or bluexe2x80x94and is driven by appropriate electronic circuitry. Conventional projectors produce images with a resolution determined by the number of pixels. The apparent resolution of the image, which is the resolution of the image as it is perceived by a human viewer, is the same as the physical or actual resolution of the LCD panels used to generate the image in the projection system. Low apparent resolution results in distortion or disappearance of small details. These effects are especially noticeable where the projected image is stationary because the observer has time to scan the whole image.
The major difficulty in manufacturing such projectors is to obtain LCD panels of sufficient resolution with minimal defects. The resolution of LCD panels has increased over the years from a typical 640xc3x97480 pixels to 800xc3x97600 pixels, and lately to 1,024xc3x97768 pixels. The yield when producing such LCD panels is relatively low, creating problems in manufacturing. The higher the resolution, the worse the yield. Projectors with even more pixels, such as 1280 or 1600, exist, but they are not popular because the prices are excessive.
Fergason (U.S. Pat. No. 5,715,029) describes one method for increasing the apparent resolution of images produced by LCD panels of low physical resolution. The Fergason system uses polarized light and birefringent materials to horizontally and vertically displace the projected image. If the displacement is performed rapidly enough, a human observer will view the displaced images as a superposition of all of the images. This superposition is claimed to appear to the human observer to have quadruple the resolution of the image that would be projected by a projector with the same LCD panels but which did not use his invention.
A limitation of the Fergason invention is that the shifting of the images is binary in nature. The image can only be shifted between a finite number of discrete locations. This creates a problem due to the manner in which LCD displays project images. An LCD display refreshes a projected image one line at a time. When a sequence of images is rapidly projected one after the other, then at any given instant the image being projected by the system is likely to contain pixels from the image currently being projected and unrefreshed pixels from the image that has previously been projected. In systems that use discrete displacements, the displacement of the images cannot follow the refresh of the LCD panel as it proceeds down the screen. Therefore, the unrefreshed pixels from the previous image will appear in the wrong place when the images are superimposed, corrupting the perceived image. Consequently, the Fergason invention is capable of increasing the apparent resolution of a projector (purportedly by a factor of four relative to its physical resolution); however, it is not capable of doing so without corrupting the image perceived by a human observer.
Accordingly, it is desirable to develop a new display system that could achieve images with high apparent resolution using LCD panels of lower physical resolution and where the displacement of the images is coordinated with the refresh function of the LCD display so that the projected image is not corrupted.
In light of the foregoing, the present invention provides a system for projecting images of high apparent resolution using a conventional projector with a low physical resolution without corrupting the projected image.
To accomplish these effects in accordance with the invention, as embodied herein, the display system comprises an optical projection system for projecting a plurality of pixels, an opto-mechanical system having a deflector for deflecting the pixels, a preprocessor for generating a plurality of rotationally offset lower resolution images from a high resolution image, and a control system for controlling deflection of the projected image and synchronizing the circular deflection of the projected image with the rotational offset of the low resolution images.
In one particular embodiment a conventional low resolution projector is utilized in combination with the present invention to substantially increase the resolution of the displayed image. The apparent high resolution projected image is produced by creating a plurality of successively rotationally offset low resolution images from a stored high resolution image and then projecting these slightly different and slightly rotationally displaced low resolution images in quick succession (60 or more per second) while simultaneously opto-mechanically deflecting the pixels of the low resolution images in a circular path on the projection screen. A control circuit synchronizes the motion of the pixels on the screen with the low resolution image that is rotationally offset in a corresponding manner.
By means of this coordination the images are effectively fused in the visual system of the viewer. Experiments with human viewers have shown that images formed without such coordination are unacceptable and do not achieve the result of increased visual resolution. Another advantage of the present system results from a xe2x80x9csmearing effectxe2x80x9d of the rotation. This results from the way a screen is refreshed. Once a given pixel is energized, it displays the same image until refreshed. Therefore, the pixels which are energized to generate a first image will stay on the screen until refreshed with the information from the second image, thus they will be slightly shifted by the deflection of the opto-mechanical system during that time. Therefore, they, so to speak, smear a very minute amount. It has been found that this effect contributes to the smoothness of the image.
Because the sequence of fixed images is projected in quick sequence (60+/sec), all a viewer perceives is a single high resolution image, and not the distinct, low resolution images superimposed by the projection system of the present invention. Further, if the refresh rate of the projector system is 80 per second, each of the four images will be displayed 20 times a second. Thus, by circulating the pixels of the projector on the screen in synchronism with the circulation of the rotational raster grid that produces the four successive images, an increase of the visual resolution can be achieved which doubles along each line and along each column of the raster. This results in the visual effect of a raster having four times as many pixels as any single, low resolution image which the projector can display at any given time.
Additional features of the invention will occur to those skilled in the art, the present invention includes all such equivalents and modifications, and is only limited by the scope of the claims.